Worm wheel of electric power steering apparatus

ABSTRACT

A worm wheel of an electric power steering apparatus includes: an inner wheel coupled to a steering shaft; an outer wheel disposed outside an outer circumference of the inner wheel and having a plurality of teeth on an outer circumferential surface to be engaged with a worm of a worm shaft; and a damper interposed between the inner wheel and the outer wheel.

CROSS REFERENCE TO RELATED APPLICATION

This application claims the benefit of priority to Korean PatentApplication No. 10-2017-0129100, filed on Oct. 10, 2017, which is herebyincorporated by reference for all purposes as if fully set forth herein.

TECHNICAL FIELD

The present disclosure relates to a worm wheel of an electric powersteering apparatus, and more specifically, to a worm wheel of anelectric power steering apparatus, in which a damper is inserted andinterposed between an inner wheel and an outer wheel of a worm wheelsuch that the worm wheel absorbs torsional load transmitted to a wormshaft from a steering shaft through the worm wheel.

BACKGROUND

Generally, a vehicle is equipped with a steering system by which adriver can intentionally change a traveling direction. The steeringsystem is an auxiliary system configured to arbitrarily change arotating center about which a front wheel of a vehicle pivots to drivethe vehicle in a direction desired by the driver.

Such a steering system of a vehicle includes a Motor-Driven PowerSteering (MDPS) in which steering power is controlled by a motor, and anelectronic control unit precisely drives the motor according totraveling conditions detected by various sensors such as a vehicle speedsensor and a steering torque sensor, a torque generated by the motor istransmitted to a steering column or pinion through a reducer tosupplement the steering power of the driver who manipulates a steeringwheel connected to the steering column and pinion.

Accordingly, the MDPS provides steering performance which allows thedriver to maintain the most optimum steering conditions by providing alight and convenient steering state at low speeds and a heavy and stablesteering state at high speeds, to respond to a sudden emergencysituation through rapid steering, and the like.

Electric power steering systems may be classified into various kindsbased on a position in which a steering column is positioned, and theelectric power steering system is a system in which a motor including areducer is installed around a steering column for fixing a steeringshaft connecting a steering wheel of a driver's seat and a gear box of alower portion of a vehicle to a vehicle body or around the gear box inwhich a pinion coupled to a rack bar is embedded, and rotating power ofthe steering wheel manipulated by the driver is transmitted to the rackbar by the reducer of the motor.

When the vehicle, to which the above-described column type electricpower steering is applied, travels, since reversely input load isapplied due to factors such as impacts transmitted from a road surface,or abrasion gradually occurs between contact portions of rotating partsin a structure in which gears are engaged to transmit rotating power,and particularly, a gap of a worm shaft increases in an axial direction,rattle noise inevitably occurs at a portion in which the worm shaft andthe worm wheel are engaged and rotated.

A gap prevention unit configured to press against a worm shaft to removea gap between the worm shaft and a worm wheel generally using a rattlespring has been used to prevent the above-described phenomenon.

Accordingly, the conventional column type electric power steeringgenerally includes a unit for preventing the above described rattlephenomenon, and such a unit is formed by supplementing the gap betweenthe worm shaft and the worm wheel gear, and has a structure in which,for example, rubber members are put in both ends of the worm wheel orthe worm wheel is tilted.

In related art, there is a rattle noise preventing type motor drivenpower steering system including a taper slider in which a gap preventionunit configured to prevent generation of a gap between a worm shaftrotated by a motor configured to convert steering power of a driver torotating power and a worm wheel configured to transmit the steeringpower to operate a gear box connected to the steering shaft is insertedinto a space between a support bearing coupled to an end portion of theworm shaft rotated by the motor supplementing the steering power and aninner side surface of a housing accommodating the worm wheel engagedwith the worm shaft and rotated to transmit the rotating power to thesteering shaft connected to the gear box, and continuously pressesagainst the worm shaft.

In another related art, there is electric power steering systemincluding a worm shaft part including a worm gear, a worm wheel part inwhich an outer circumferential surface is engaged with the worm gear androtated, a hub portion engaged with an inner circumferential surface ofthe worm wheel part and rotated, a motor part configured to rotate theworm shaft part, and a vibration prevention part installed in the hubportion and configured to suppress noise.

However, a rattle prevention structure related to a conventional wormshaft includes a gap prevention unit, since the structure continuouslypresses against the worm shaft, an external impact is directlytransmitted to the worm shaft, and thus, components may be easilydamaged due to the repeated impacts.

In addition, the rattle prevention structure applied to the conventionalworm wheel includes the vibration prevention part including a viscousfluid and a cover plate to suppress noise, but in this case, the viscousfluid can be contaminated and a normal vibration prevention function ofthe viscous fluid can be removed when the viscous fluid leaks to theoutside, and it is cumbersome to frequently inject the viscous fluidinto the rattle prevention structure.

SUMMARY

An aspect of the present disclosure is to provide a worm wheel of anelectric power steering apparatus in which a damper is inserted anddisposed such that the worm wheel absorbs torsional load transmitted toa worm shaft from a steering shaft through the worm wheel to reduce thetorsional load when a vehicle travels on a harsh road.

Another aspect of the present disclosure is to provide a worm wheel ofan electric power steering apparatus which reduces deformation andabrasion of a worm of a worm shaft and a gear part of the worm wheel byreducing vibrations caused by torsional load.

Besides the above-described technical objectives of the presentdisclosure, features and advantages of the present disclosure will bedescribed below, or will be clearly understood by those skilled in theart through the technology and description.

According to an exemplary embodiment of the present disclosure, a wormwheel of an electric power steering apparatus includes: an inner wheelcoupled to a steering shaft; an outer wheel disposed outside an outercircumference of the inner wheel and having a plurality of teeth on anouter circumferential surface to be engaged with a worm of a worm shaftis formed; and a damper interposed between the inner wheel and the outerwheel.

In the worm wheel of the electric power steering apparatus according tothe exemplary embodiment of the present disclosure, since the damper isinserted and interposed between the inner wheel and the outer wheel ofthe worm wheel, in a case in which a vehicle travels on a harsh road,the worm wheel can absorb torsional load transmitted from the steeringshaft to the worm shaft through the worm wheel to reduce the torsionalload.

In addition, by reducing vibrations caused by the torsional load,deformation and abrasion of the worm wheel can be reduced.

Accordingly, abrasion of a worm of the worm shaft and a gear part of theworm wheel can be reduced, and finally rattle noise caused by theabrasion of the worm of the worm shaft and the gear part of the wormwheel can be reduced so that a gap prevention unit may not be required.

Since the damper is inserted into and disposed in the worm wheel of theelectric power steering apparatus according to the exemplary embodimentof the present disclosure, in a case in which a vehicle travels a harshroad, the worm wheel can absorb torsional load transmitted form thesteering shaft to the worm shaft through the worm wheel to reduce thetorsional load.

Accordingly, abrasion of the worm of the worm shaft and the gear part ofthe worm wheel can be reduced, and finally rattle noise caused by theabrasion of the worm of the worm shaft and the gear part of the wormwheel can be reduced so that a gap prevention unit may not be required.

Effects which can be obtained from the present disclosure are notlimited to the above-described effects, and other effects which are notdescribed above will be clearly understood by those skilled in the artthrough the following description.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other aspects, features and advantages of the presentdisclosure will be more apparent from the following detailed descriptiontaken in conjunction with the accompanying drawings, in which:

FIG. 1 is a cross-sectional view illustrating a reducer of an electricpower steering apparatus according to an exemplary embodiment of thepresent disclosure;

FIG. 2 is an exploded perspective view illustrating a worm wheel of theelectric power steering apparatus according to an exemplary embodimentof the present disclosure;

FIG. 3 is a cross-sectional view illustrating a damper of the worm wheelaccording to an exemplary embodiment of the present disclosure; and

FIG. 4 is a cross-sectional view illustrating the worm wheel of theelectric power steering apparatus according to an exemplary embodimentof the present disclosure.

DETAILED DESCRIPTION OF THE EXEMPLARY EMBODIMENTS

Hereinafter, embodiments that are easily performed by those skilled inthe art will be described in detail with reference to the accompanyingdrawings. The embodiments of the present disclosure may be implementedin several different forms and are not limited to the embodimentsdescribed herein.

Throughout this specification, when a part is referred to as being“connected” to another part, it includes “directly connected” and“electrically connected” via an intervening part. When a certain part“includes” a certain component, this does not exclude other componentsunless explicitly described otherwise, and other components may in factbe included.

Hereinafter, embodiments that are easily performed by those skilled inthe art will be described in detail with reference to the accompanyingdrawings. However, the embodiments of the present disclosure may beimplemented in several different forms, and are not limited to theembodiments described herein.

FIG. 1 is a cross-sectional view illustrating a reducer of an electricpower steering apparatus according to an exemplary embodiment of thepresent disclosure.

Referring to FIG. 1, a reducer 100 has a structure having a worm shaft110 formed of a metal material and having a central portion in which aworm 120 is disposed; worm bearings 130 installed on both ends of theworm shaft 110 to support the worm shaft 110 which is connected with amotor shaft 140; and a motor 150 rotating the worm shaft 110.

A worm wheel 200 is disposed outside the worm 120 in a circumferentialdirection thereof as a reducer to be engaged with the worm 120 formed atthe central portion of the worm shaft 110.

The worm wheel 200 is installed on a steering shaft 300 configured totransmit rotating power of a steering wheel manipulated by a driver totransmit rotating power of the worm shaft 110 generated by driving ofthe motor 150 to the steering shaft 300.

When the steering shaft 300 generates rotating power by an externalimpact and transmits the rotating power to the worm wheel 200, the wormwheel 200 transmits the rotating power transmitted through the steeringshaft 300 to the worm shaft 110.

The worm shaft 110 and the worm wheel 200 are engaged through a wormgear method, and are installed in a housing 160 to be protected fromoutside environments.

FIG. 2 is an exploded perspective view illustrating the worm wheel ofthe electric power steering apparatus according to an exemplaryembodiment of the present disclosure.

Referring to FIG. 2, the worm wheel 200 includes an inner wheel 210coupled to the steering shaft 300, an outer wheel 230 disposed outsidean outer circumference of the inner wheel 210 and having an outercircumferential surface on which a gear 231 engaged with the worm 120 ofthe worm shaft 110 is formed, and a damper 220 inserted and interposedbetween the inner wheel 210 and the outer wheel 230.

When the worm shaft 110 or steering shaft 300 transmits rotating powerto the worm wheel 200, the inner wheel 210 and the outer wheel 230rotate together. When rotating power transmitted to the worm wheel 200suddenly increases (for example, when a vehicle travels a harsh road,and load transmitted to a rack bar (not shown) and the steering shaft300 from a wheel suddenly increases), twist may occur between the innerwheel 210 and the outer wheel 230.

The damper 220 absorbs torsional load generated between the inner wheel210 and the outer wheel 230, reduces the torsional load transmitted fromthe steering shaft 300, and transmits the torsional load to the wormshaft 110.

In addition, the damper 220 may reduce vibrations transmitted to theworm shaft 110 by absorbing the torsional load of the worm wheel 200 toprevent deformation and damage of the worm shaft 110 and the worm wheel200.

FIG. 3 is a cross-sectional view illustrating the damper of the wormwheel according to an exemplary embodiment of the present disclosure.

Referring to FIG. 3, the damper 220 includes a body 221 for a dampingfunction when the worm wheel rotates, and a fixing part 226 configuredto couple the damper to the outer wheel and the inner wheel.

The body 221 has a closed ring shape and includes at least oneprotruding portion 222 protruding outward in a diameter direction and atleast one recessed portion 223 recessed inward in the diameterdirection.

The body 221 may be formed of a metal material having a predeterminedelastic force, and a plurality of protruding portions 222 and aplurality of recessed portions 223 are alternately formed and connectedin a circumferential direction so that repeated irregularities may beformed.

That is, the plurality of protruding portions 222 are connected to theplurality of recessed portions 223 in a ring shape to form the body 221.

The fixing part 226 may include inner wheel fixing parts 227 forcoupling the damper 220 and the inner wheel 210 and outer wheel fixingparts 228 for coupling the damper 220 and the outer wheel 230.

The inner wheel fixing part 227 protrudes inward from an innercircumferential surface of the protruding portion 222 in the diameterdirection, and the outer wheel fixing part 228 protrudes outward from anouter circumferential surface of the protruding portion 222 in thediameter direction.

In addition, the inner wheel fixing part 227 and the outer wheel fixingpart 228 may be connected in a zigzag shape.

The inner wheel fixing part 227 is accommodated inside the inner wheeland connects the protruding portions 222 of the body 221. That is, bothend portions of the inner wheel fixing part 227 may be bent and areconnected to any one protruding portion and another adjacent protrudingportion.

That is, one end of the inner wheel fixing part 227 is connected to anyone protruding portion 222 among the plurality of protruding portions,and the other end of the inner wheel fixing part 227 is connected to theadjacent protruding portion 222 in the circumferential direction.

Referring to FIG. 3, the inner wheel fixing part 227 may substantiallyhave a cross section in a “└┘” shape. For example, one end of the innerwheel fixing part 227 protrudes inward (toward the steering shaft) froman inner circumferential surface 225 of any one protruding portion 222of the body 221, and the other end thereof is connected to an innercircumferential surface of the adjacent protruding portion 222. Here,the inner wheel fixing part 227 may spaced apart from the innercircumferential surface of the recessed portion 223 of the body 221.

In addition, one ends and the other ends of the inner wheel fixing parts227 connected to the protruding portions 222 extend inward in thediameter direction and are bent in opposite circumferential directionssuch that the inner wheel fixing parts 227 are connected.

The outer wheel fixing part 228 is disposed outside the inner wheel andconnects the protruding portions 222 of the body 221. That is, both endportions of the outer wheel fixing part 228 may be bent, and the bothend portions may be connected to any one protruding portion and anotheradjacent protruding portion.

That is, one end of the outer wheel fixing part 228 is connected to anyone protruding portion 222 among the plurality of protruding portions,and the other end of the outer wheel fixing part 228 is connected to theadjacent protruding portion 222 in the circumferential direction.

Referring to FIG. 3, the outer wheel fixing part 228 may substantiallyhave a cross section in a “┌┐” shape. For example, one end of the outerwheel fixing part 228 protrudes outward (toward the worm shaft) from anouter circumferential surface 224 of any one protruding portion 222 ofthe body 221, and the other end thereof is connected to an outercircumferential surface of the adjacent protruding portion 222.

In addition, one end portions and the other end portions of the outerwheel fixing parts 228 connected to the protruding portions 222 extendinward, and are bent in opposite circumferential directions such thatthe outer wheel fixing parts 228 are connected.

The inner wheel fixing part 227 and the outer wheel fixing part 228 arealternately disposed in a circumferential direction of the fixing part226.

In addition, one end and the other end of the inner wheel fixing part227 are disposed at positions corresponding to one end and the other endof the outer wheel fixing part 228.

FIG. 4 is a cross-sectional view illustrating the worm wheel of theelectric power steering apparatus according to an exemplary embodimentof the present disclosure.

As illustrated in FIG. 4, the damper 220 is inserted and interposedbetween the inner wheel 210 and the outer wheel 230, the inner wheelfixing part 227 is coupled to the inner wheel 210, and the outer wheelfixing part 228 is coupled to the outer wheel 230.

The body 221 of the damper 220 may be formed to be accommodated insidethe inner wheel 210. That is, the outer circumferential surface of theprotruding portion 222 may be matched with the outer circumferentialsurface of the inner wheel 210, or the outer circumferential surface ofthe protruding portion 222 may be positioned inside and spaced apartfrom the outer circumferential surface of the inner wheel 210.

The inner wheel 210 may be formed through an injection molding method toaccommodate the damper 220, and the outer wheel 230 may be formedthrough an injection molding method outside the inner wheel 210accommodating the damper 220.

The damper 220 serves as a spring configured to absorb torsional loadbetween the inner wheel 210 and the outer wheel 230, and serves toreduce vibrations caused by the torsional load.

As described above, in the worm wheel 200 of the electric power steeringapparatus according to the an exemplary embodiment of the presentdisclosure, since the damper 220 is inserted and interposed between theinner wheel 210 and the outer wheel 230 of the worm wheel 200, in a casein which a vehicle travels on a harsh road, the worm wheel 200 mayabsorb torsional load transmitted from the steering shaft 300 to theworm shaft 110 through the worm wheel 200 to reduce the torsional load.

In addition, by reducing vibrations caused by the torsional load,deformation and abrasion of the worm 120 of the worm shaft 110 and thegear 231 of the worm wheel 200 can be reduced.

Accordingly, abrasion of the worm 120 of the worm shaft 110 and the gear231 of the worm wheel 200 can be reduced, and finally, rattle noisecaused by the abrasion of the worm 120 of the worm shaft 110 and thegear 231 of the worm wheel 200 can be reduced so that a gap preventionunit may not be required.

It will be understood by those skilled in the art that the disclosuremay be performed in other concrete forms without changing thetechnological scope and essential features. Therefore, theabove-described embodiments should be considered in a descriptive senseonly and not for purposes of limitation. The scope of the presentdisclosure is defined not by the detailed description but by theappended claims, and encompasses all modifications and alterationsderived from meanings, the scope and equivalents of the appended claims.

What is claimed is:
 1. A worm wheel of an electric power steeringapparatus, comprising: an inner wheel coupled to a steering shaft; anouter wheel disposed outside an outer circumference of the inner wheeland having a plurality of teeth on an outer circumferential surface tobe engaged with a worm of a worm shaft; and a damper interposed betweenthe inner wheel and the outer wheel.
 2. The worm wheel of claim 1,wherein the damper comprises: a body comprising at least one protrudingportion protruding outward in a radial direction and having a ringshape; and a fixing part disposed on at least any one side of an outerside and an inner side of the body and configured to fix the inner wheeland the outer wheel to the body.
 3. The worm wheel of claim 2, whereinthe body further comprises at least one recessed portion recessed inwardin the radial direction.
 4. The worm wheel of claim 3, wherein each ofthe protruding portion and the recessed portion is provided in plural,and wherein the plurality of protruding portions and the plurality ofrecessed portions are alternately disposed and connected in acircumferential direction.
 5. The worm wheel of claim 2, wherein thefixing part comprises an inner wheel fixing part protruding inward froman inner circumferential surface of the protruding portion in the radialdirection.
 6. The worm wheel of claim 5, wherein each of the protrudingportion and the recessed portion is provided in plural, and wherein afirst end of the inner wheel fixing part is connected to a firstprotruding portion among the plurality of protruding portions, and asecond end of the inner wheel fixing part is connected to a secondprotruding portion adjacent the first protruding portion in thecircumferential direction,
 7. The worm wheel of claim 6, wherein thefirst and second ends of the inner wheel fixing part extend inward inthe radial direction from the inner circumferential surface of the firstand second protruding portions, respectively, and then are bent towardeach other in the radial direction in opposite circumferentialdirections to be connected to each other.
 8. The worm wheel of claim 5,wherein the fixing part further comprises an outer wheel fixing partprotruding outward from an outer circumferential surface of theprotruding portion.
 9. The worm wheel of claim 8, wherein a first end ofthe outer wheel fixing part is connected to a third protruding portionamong the plurality of protruding portions, and a second end of theouter wheel fixing part is connected to a fourth protruding portionadjacent the third protruding portion in the circumferential direction.10. The worm wheel of claim 9, wherein the first and second ends of theouter wheel fixing part extend outward from the outer circumferentialsurface of the protruding portion in the radial direction, and then arebent toward each other in the circumferential direction to be connectedto each other.
 11. The worm wheel of claim 8, wherein each of the innerwheel fixing part and the outer wheel fixing part is provided in plural,and wherein each of the plurality of inner wheel fixing parts and eachof the plurality of outer wheel fixing parts are alternately disposed inthe circumferential direction.
 12. The worm wheel of claim 11, whereineach end of the inner wheel fixing part is disposed to be correspond toeach end of the outer wheel fixing part, respectively.
 13. The wormwheel of claim 2, wherein the body of the damper is accommodated insidethe inner wheel.
 14. The worm wheel of claim 2, wherein an outercircumferential surface of the protruding portion of the body of thedamper corresponds to an outer circumferential surface of the innerwheel.
 15. The worm wheel of claim 2, wherein an outer circumferentialsurface of the protruding portion of the body of the damper is disposedinside and spaced apart from an outer circumferential surface of theinner wheel.
 16. The worm wheel of claim 1, wherein the damper has aclosed ring shape.
 17. The worm wheel of claim 1, wherein the damper isformed of a metal material.
 18. The worm wheel of claim 7, wherein theinner wheel fixing part has a cross section having a “U” shape.
 19. Theworm wheel of claim 10, wherein the outer wheel fixing part has a crosssection having an inversed “U” shape.
 20. The worm wheel of claim 10,wherein an outer diameter of the damper is greater than an innerdiameter of the outer wheel, and an inner diameter of the damper issmaller than an outer diameter of the inner wheel.